On head microelectronics for write synchronization

ABSTRACT

The presently disclosed technology teaches integrating disc drive electronics into a transducer head. Decreased electrical transit times and data processing times can be achieved by placing the electronics on or within the transducer head because electrical connections may be made physically shorter than in conventional systems. The electronics may include one or more of a control system circuit, a write driver, and/or a data buffer. The control system circuit generates a modified clock signal that has a fixed relation to phase and frequency of a bit-detected reference signal that corresponds to positions of patterned bits on the disc. The write driver writes outgoing data bits received from an external connection to off-head electronics directly to the writer synchronized with the modified clock signal. The data buffer stores and converts digital data bits sent from the off-head electronics to an analog signal that is synchronized with the modified clock signal.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims benefit of priority toU.S. patent application Ser. No. 15/827,230 filed Nov. 30, 2017 and U.S.patent application Ser. No. 12/571,959, filed Oct. 1, 2009, now U.S.Pat. No. 9,842,612, all of which are incorporated herein by reference intheir entireties.

BACKGROUND

During a write to a receiving media by a transducer head, the transducerhead uses a magnetic read sensor to read up-track of the writinglocation to assure the desired data track is targeted during the writeoperation. As media areal or bit density increases, maintaining aconsistent track between the read sensor and a writing pole on thetransducer head becomes increasingly difficult.

Additionally, in the continuing effort to increase areal density, mediawith arrays or patterned cells have been designed where each cell canhold a bit of data (bit patterned media (BPM)). On such BPM, data may bestored in individual cells along a data track defined by the patternedbits. However, each patterned bit is temporally synchronized with eachdata bit. Otherwise, data insertion may occur on an incorrect patternedbit or a patterned bit may be skipped for data writing. Therefore, oneof the challenges with BPM is placing the head over the bit of interestaccurately during writing. This is especially challenging due to thesmall size of the patterned bits (e.g. 1 nano-meter wide) and timingcontrol requirements in a disc system rotating at high speeds (e.g.20-50 pico-seconds per rotation). Other media forms exhibit similarchallenges.

SUMMARY

The presently disclosed technology teaches a method of recording data tobit locations on a storage media. A transducer head is provided thatincludes on-head control system circuitry. A clock signal issynchronized with a bit-detected reference signal using the on-headcontrol system circuitry to generate a modified clock signal that issynchronized with the bit locations on the storage media. Data receivedfrom off-head electronics is then recorded to the bit locations on thestorage media using the modified clock signal.

In another implementation, the presently disclosed technology teaches atransducer head with an on-head bit detector configured to detect areference signal corresponding to bit locations on a storage media. Thetransducer head also includes an on-head control system circuitconfigured to synchronize a clock signal with the bit-detected referencesignal to generate a modified clock signal that is synchronized with thebit locations. The transducer head also includes an on-head writerconfigured to record data received from off-head electronics to the bitlocations on the storage media.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter. These andvarious other features and advantages will be apparent from a reading ofthe following detailed description.

BRIEF DESCRIPTIONS OF THE DRAWINGS

The described technology is best understood from the following DetailedDescription describing various implementations read in connection withthe accompanying drawings.

FIG. 1 illustrates a plan view of an implementation of BPM on a mediawith a transducer head situated on an end of an actuator assembly.

FIG. 2 is a cross sectional view illustrating microelectronicsintegrated in an example transducer head positioned relative to a media.

FIG. 3 illustrates an elevation view of an implementation of patternedbits on a media with a transducer head incorporating a metallicelectrode, a bit detector, and a preamplifier.

FIG. 4 illustrates an elevation view of another implementation ofpatterned bits on a media with a transducer head incorporating ametallic electrode and a capacitance circuit.

FIG. 5 is a flow diagram illustrating an on-head phase-locked loop (PLL)control scheme.

FIG. 6 is a flow diagram illustrating an on-head phase-locked loop (PLL)control scheme with an on-head write driver.

FIG. 7 is a flow chart illustrating operations for using an on-headphase-locked loop and an on-head write driver to synchronize writing ofdata bits to patterned bits on a media.

FIG. 8 illustrates a plan view of an example disc drive.

DETAILED DESCRIPTIONS

In magnetic storage media, a magnetic recording layer includes a thinfilm of a magnetic alloy that forms random nanometer-scale grains thatbehave as independent magnetic elements. Each written bit is made up ofmany of these random grains. In bit patterned media (BPM), the magneticlayer is pre-patterned with an ordered array of patterned bits, eachpatterned bit capable of storing an individual data bit. The BPM may bepre-patterned through various procedures such as, but not limited to,lithography, ion-milling, etc. Other storage media types exist,including digital recording tape and floppy disks. The presentlydisclosed technology may be applicable to the various magnetic mediastorage types.

The time between bit detection using a read sensor and/or a bit detectorand bit writing is critical in the correct writing of data to bitlocation on a media (e.g., a disc drive). Present magnetic recordingsystems typically require detected data to be sent from a transducerhead to processing electronics located elsewhere in a media driveassembly via long electronic lines. Further, power used to write data tothe media is sent from the processing electronics via the long electriclines back to the transducer head. The time required and errors involvedin sending data from the transducer head to the off-head processingelectronics and back to the transducer head is significant when comparedto a phase coherence of BPM writing.

According to the presently disclosed technology, electronics that arepositioned off-head in the current state of the art are integrated intothe transducer head to improve synchronization of data writing withpatterned bit locations on the media. Decreased electrical transit timesand data processing times can be achieved by placing the electronics onor within the transducer head because electrical connections between theprocessing electronics and the read sensor(s), bit detector(s), and/orwriter (also located one the transducer head) may be made physicallyshorter than in conventional systems. Physically shorter electricalconnections between electronic components can decrease electricaltransit times and data processing times by providing a shorter path forelectrons to flow between the electronic components.

FIG. 1 illustrates a plan view of an implementation of BPM on a media108 with a transducer head 120 situated on an end of an actuatorassembly 110. Referring specifically to View A, media 108 rotates abouta media axis of rotation 112 during operation. Further, media 108includes an outer diameter 102 and inner diameter 104 between which area number of data tracks 106, illustrated by circular dotted lines. Datatracks 106 are substantially circular and are made up of regularlyspaced patterned bits 122.

Information may be written to and read from the patterned bits 122 onthe media 108 through the use of the actuator assembly 110, whichrotates during a data track 106 seek operation about an actuator axis ofrotation 114 positioned adjacent the media 108. A transducer head 120mounted on the actuator assembly 110 at an end distal the actuator axisof rotation 114 flies in close proximity above the surface of the media108 during media operation.

In one implementation, the transducer head 120 as detailed in View Butilizes a read sensor 116 to perform a read-before-write process tomaintain a transducer head 120 position over a desired data track 106.The read-before-write process is performed by reading magnetic signalsfrom grains on the media 108 and determining a location of a writer 118with respect to the desired data track 106 from the detected data.

In another implementation, transducer head 120 includes one or more bitdetectors, which will be discussed in more detail with respect to FIGS.2-6. A bit detector in lieu of or in addition to the read sensor 116offers improved accuracy and speed in determining a location of thewriter 118 from a waveform reflected from the patterned bits 122 to thetransducer head 120.

In yet another implementation, transducer head 120 includes one or moreelectrical wires containing spin-polarized currents which will bediscussed in more detail with respect to FIG. 2. A spin angular momentumsensor in lieu of or in addition to the read sensor 116 offers improvedaccuracy and speed in determining a location of the writer 118 bydetecting changes in spin properties of the one or more spin-polarizedcurrents when the electrical wires pass in close proximity to thepatterned bits 122.

The transducer head 120 is shown in greater detail in View B of FIG. 1.Transducer head 120 is shown with the read sensor 116, the writer 118,on-head microelectronics 128, bond pads 126, and data signal wires 124electrically connecting the on-head microelectronics 128 to the bondpads 126. The read sensor 116 is configured to read data from thepatterned bits 122 on the media 108 and the writer 118 is configured towrite data to the patterned bits 122 on the media 108.

Referencing FIG. 1, data to be written to the patterned bits 122 is sentfrom the off-head electronics to bond pads 126 attached to the exteriorof the transducer head 120. The data is then sent to the on-headmicroelectronics 128 via the data signal wires 124 within the transducerhead 120. In some implementations, timing data from the read sensor(s)is sent to the on-head microelectronics 128 for processing. Then theprocessed timing data may then continue to other on-head components orbe sent to the bond pads 126 via the data signal wires 124. The off-headelectronics may then read the processed timing data from the bond pads126. In still further implementations, data read from the media may betransmitted directly to the bond pads 126 and then the off-headelectronics without any connection to the on-head microelectronics 128.

FIG. 2 is a cross sectional view illustrating microelectronicsintegrated in an example transducer head 220 positioned relative to amedia 208. Media 208 is made of a substrate material 230 (e.g. aluminum,glass, or ceramic). A thin coating known as an underlayer 232 isdeposited on top of the substrate material 230. The underlayer 232 isoften deposited by a vacuum deposition process (e.g. magnetronsputtering) and has a layered structure consisting of various metallicalloys arranged to optimize control of a crystallographic orientationand grain size of a magnetic medium 234 positioned on top of theunderlayer 232. The magnetic medium 234 is divided into smallsub-micrometer sized regions (e.g. groups of grains or patterned bits),each of which is used to represent a single binary bit of information. Amedia overcoat 236 that protects the magnetic medium 234 from damage isdeposited on top of the magnetic medium 234, often using the same vacuumdeposition process as the underlayer 232. Finally, a thin polymericlubricant layer 238 is deposited on top of the media overcoat 236, oftenby dipping the media 208 is a solvent solution. Even after the media 208is buffed by various processes to eliminate defects and smooth the mediasurface, a media roughness facing the transducer head 220 still existsthat may be measured with reference to patterned bit size.

Transducer head 220 is made of a substrate material upon which at leasta read sensor 216, a writer 218, on-head microelectronics 228, bond pads226, and data signal wires 224 electrically connecting the on-headmicroelectronics 228 to the bond pads 226 are mounted. The read sensor216, writer 218, on-head microelectronics 228, bond pads 226, and datasignal wires 224 are mounted within and/or on the surface of thetransducer head 220.

In one implementation, the on-head microelectronics 228 includes acontrol system, a write driver, and a data buffer. In otherimplementations, the on-head microelectronics 228 includes the controlsystem, write driver, or the data buffer. In still otherimplementations, the on-head microelectronics 228 includes any two ofthe control system, write driver, and data buffer. In implementationswhere the control system, write driver, and/or data buffer are not apart of the on-head microelectronics, the control system, write driver,and/or data buffer are located off-head or not included in the system atall.

In another implementation, the transducer head 220 also incorporates abit detector 250 configured to detect a waveform generated by anoscillator that is reflected off of a bit of interest on the media 208.The oscillator may be any electronic circuit capable of producing arepetitive electronic signal (e.g. a microwave) and may take the form ofa bonded microchip with a delivery system in the form of a wire or aslot line.

In one implementation, the bit detector 250 is any device configured todetect the presence of the reflected waveform. In anotherimplementation, the bit detector 250 is configured to detect wave shape,wave level, amplitude, frequency, wavelength, and/or other propertiesspecific to the reflected waveform. The presence of the reflectedwaveform and/or various properties of the reflected waveform detected bythe bit detector 250 may be used to determine the location of the bit ofinterest on the media 208.

In another implementation, a spin-polarized current injector is used inlieu of the oscillator and the bit detector 250 is a spin angularmomentum sensor 250. Current from the spin-polarized current injectorpasses through the transducer head 220 via an electrical wire in closeproximity to the bit of interest. A magnetic field possessed by the bitof interest interacts with (i.e. transfers spin angular momentum to) thespin-polarized current. The spin angular momentum sensor 250 thendetects changes in spin properties of the spin-polarized current.

The spin angular momentum sensor, which can be used as an implementationof a bit detector 250, is a device configured to detect the presence ofspin-polarized current. Further, the spin angular momentum sensor 250may be configured to detect spin magnitude, spin direction, and/or otherproperties specific to the spin-polarized current. Still further, thespin angular momentum sensor 250 may be configured to detect a frequencyof alternating spin species. The presence of spin-polarized currentand/or various properties of the spin-polarized current detected by thespin angular momentum sensor may be used to determine the location ofthe bit of interest on the media 208.

In some implementations, such as the implementation shown in FIG. 2, thebit detector 250 is positioned down-track of the writer 218. In otherimplementations, the bit detector 250 is positioned up-track of thewriter 218. In yet other implementations, there are multiple bitdetectors 250 positioned up-track and/or down-track of the writer 218.

Similar to the media 208, the surface of the transducer head 220 facingthe media 208 is covered with a head overcoat 240 that protects the readsensor 216, writer 218, and other components of the transducer head 220from damage. The head overcoat 240 is and is often deposited using thesame vacuum deposition process as the media overcoat 236. Further, thesurface of transducer head 220 also has a head roughness that may bemeasured with reference to patterned bit size. The distance between themedia overcoat 236 and the head overcoat 240 is referred to herein asclearance 242 and the distance between the bottom of the writer 218 andthe top of the magnetic medium 234 is referred to herein as thetransducer spacing 244.

In the implementation shown in FIG. 2, the media 208 moves in a left toright fashion (i.e., clockwise when viewed from above) and the on-headmicroelectronics 228 are oriented vertically and positioned up-trackfrom the read sensor 216 and the writer 218. However, other orientations(e.g. horizontal) and positions (e.g. down track from the read sensor216 and the writer 218, between the read sensor 216 and the writer 218,or above the read sensor 216 and the writer 218) of the on-headmicroelectronics 228 are contemplated. Further, the on-headmicroelectronics 228 may be positioned within the transducer head 220 ormounted on an exterior surface of the transducer head 220. Stillfurther, the on-head microelectronics 228 may have multiple componentsin different orientations and/or positions.

Positioning of the on-head microelectronics 228 may depend on processand design constraints and the specific application of the presentlydisclosed technology. For example, implementations that transfer powerfrom the on-head microelectronics 228 to the writer 218 may require theon-head microelectronics 228 to be positioned directly adjacent thewriter 218.

Several methods with varying levels of integration exist for joining theon-head microelectronics 228 to the transducer head 220. The highestlevel of integration may be achieved with thin film processingtechniques to directly manufacture the on-head microelectronics 228 inplace within the transducer head 220 during the fabrication of thetransducer head 220. At the lowest level of integration are techniqueswhich involve separately manufacturing the on-head microelectronics 228and the transducer head 220 and then joining the on-headmicroelectronics 228 and the transducer head 220 together.

When fabricated on or within the transducer head 220 using conventionaldeposition and patterning techniques during the manufacture of thetransducer head 220, the on-head microelectronics 228 may take the formof semiconductor devices (e.g. thin film transistors and diodes).Potential materials for the semiconductor devices include, but are notlimited to Si, poly-Si, SIGe, GaAs, InP, ZnO, SnO2, and other thin filmmaterials. Multiple semiconductor devices as discussed above may becombined in varying levels of complexity to form the on-headmicroelectronics 228.

A wider range of microelectronic circuitry (e.g. high performance andsophisticated microprocessors) is available for the on-headmicroelectronics 228 when the microelectronic circuitry can be bonded tothe transducer head 220 after fabrication of the transducer head 220 butbefore, during, or after the transducer head 220 is processed. Further,standard semiconductor processing techniques may be utilized and allsemiconductor substrates (e.g. Si, SOI, GaAs, and InP) are availablewhen the microelectronic circuitry is bonded to the transducer head 220after fabrication of the transducer head 220.

In a further implementation, individual microelectronic circuits arepositioned and bonded to the read sensor(s) 216 and/or writer 218 eitherduring or after fabrication of the transducer head 220. Themicroelectronic circuits may then be integrated into the transducer head220 as discussed above.

Wafer-to-wafer bonding may be used to bond fabricated on-headmicroelectronics 228 to transducer head 220 wafers. Microelectric die(s)associated with the on-head microelectronics 228 may be patterned andintegrated into the transducer head 220 using conventional processingtechniques. A result is reduced complexity by processing whole wafersrather than individual microelectronic devices and semiconductordevices.

Still referring to FIG. 2, the on-head microelectronics 228 areconnected to bond pads 226 located on an exterior surface of thetransducer head 220 via data signal wires 224. A conductive flex 246with end connectors 248 attached to the bond pads 226 allowcommunication between the on-head microelectronics 228 and electronicslocated off-head. In various implementations described with morespecificity with regard to FIGS. 3 and 4 below, the read sensor 216 andthe writer 218 are electrically connected to the on-headmicroelectronics 228 and/or the off-head electronics.

FIG. 3 illustrates an elevation view of an implementation of bitlocation 322 on a media 308 with a transducer head 320 incorporating ametallic electrode 352, a bit detector 350, and a preamplifier 358. Highfield or Fowler-Nordheim (F-N) tunneling current 354 is passed underhigh voltage from the metallic electrode 352 to BPM on the media 308. Asthe media 308 rotates, the metallic electrode 352 alternates itsalignment between orientations adjacent patterned bits 322 andorientations adjacent insulating regions 356. This alternation resultsin an alternating distance between the metallic electrode 352 and themedia (patterned bit 322 or conducting underlayer 332) and therefore amodulating tunneling current 354 corresponding to patterned bit 322locations.

In the implementation of FIG. 3, the bit detector 350 and preamplifier358 together comprise the on-head microelectronics. The bit detector 350detects the modulating tunneling current 354 and generates a timingsignal that can be used to determine a frequency of the bit locations322. In one implementation, the metallic electrode 352 can also be awriter because both the metallic electrode 352 and the writer must bealigned with the patterned bits 322 and pass very close to the media 308during data bit writing.

F-N field emission is a quantum mechanical process where electrons flowfrom a material into space under an electric field. Generally, F-Nemission creates very small electric current flows typically in therange of 10⁻⁹ to 10⁻¹² Amps between a transducer head 320 and a media308. However, the F-N emission may be amplified to create an electriccurrent with a magnitude sufficient to affect the media 308. Theamplified F-N emission may cause damage to the transducer head 320and/or media 308 if too great in magnitude and/or not timed accuratelyto correspond with bit locations 322 using a timing signal (discussedbelow).

Since the modulating tunneling current 354 is typically very small inmagnitude, the bit detector 350 may be connected to a preamplifier 358on the transducer head 320 to amplify the signal before transmission towrite driver electronics located either on-head or off-head. In oneimplementation, the output signal voltage from the preamplifier 358 isproportional to the modulating F-N current and the output signal is usedas a clock input for phase-locked loop (PLL), delay-locked loop (DLL),or other write driver control schemes. PLL control schemes are discussedin more detail below with regard to FIGS. 5 and 6.

The advantage of the implementation of FIG. 3 as compared with thecurrent state of the art is a stronger electrical signal is transmittedto processing electronics located either on-head or off-head todetermine phase requirements for the writer. The result is less error indetection of bit locations 322 and improved synchronization of thewriting of data bits to the patterned bits 322.

The voltage applied through the metallic electrode 352 is relativelyconstant with respect to bit location 322 and inter-bit insulator 356locations. However, in another implementation, the voltage could bevaried to minimize fluctuations in the tunneling current 354 due tooutside parameters (e.g. fly height). An automatic gain control (AGC)feedback amplifier may be used to control voltage of the tunnelingcurrent 354. Further, the AGC feedback amplifier could be used toindicate head to media clearance, which is important when selectingclearance values in media drive certification as well as during mediadrive operation under varying environmental conditions.

FIG. 4 illustrates an elevation view of another implementation of bitlocations 422 on a media 408 with a transducer head 420 incorporating ametallic electrode 452 and a capacitance circuit 460. Here, the metallicelectrode 452 is connected to an alternating current signal generator. Acapacitance between the metallic electrode 452 and the media 408modulates as the metallic electrode 452 alternates from a patterned bit422 location and an insulating region 456 location. This capacitancemodulation can be used to detect patterned bit 422 locations and atiming signal can be generated based on the capacitance modulation.

The capacitance circuit 460 has an oscillator 462, a tunable resonatorcircuit 464, and a voltage or current sensor 450. The oscillator 462 isconnected to the resonator circuit 464 as shown schematically in FIG. 4.When DC power is applied to the oscillator 462, the capacitance circuit460 resonates at a resonator circuit 464 frequency (e.g., approximatelyone gigahertz). The resonator circuit 464 is a conducting line coupledto the metallic electrode 452. As the metallic electrode 452 moves fromthe patterned bit 422 location to the insulating region 456 location,the capacitance between the media 408 and the metallic electrode 452changes. A resonant frequency of the resonance circuit 464 changes andthe amplitude and/or voltage of the current in the resonance circuit 464is modulated. The modulated current or voltage signal from the resonancecircuit 464 is received by the sensor 450 and can then be transmitted towrite driver electronics located either on-head or off-head.

An advantage of placing the capacitance circuit 460 on-head is that thesignal to noise ratio in the modulated current or voltage is reduced. Bymaking the capacitance circuit 460 physically closer to the bitlocations 422, the conducting lines between the capacitance circuit 460and the bit locations 422 may be made shorter than in an off-headcapacitance circuit 460 application. As the distance between thecapacitance circuit 460 and the bit locations 422 increases, signal lossin conducting lines and convolution with other microwave effects in themedia 408 assembly increases. Therefore, minimizing the distance betweenthe capacitance circuit 460 and the bit locations 422 is desirable.

FIG. 5 is a flow diagram illustrating an on-head phase-locked loop 566(PLL) control scheme. The PLL 566 is a control system that generates amodified clock signal 572 that has a fixed relation to phase andfrequency of a bit-detected reference signal 574. The PLL 566 circuitcompares frequency and phase of a clock signal and the bit-detectedreference signal 574 and iteratively adjusts the frequency of the clocksignal until the frequency and phase of the clock signal matches thefrequency and phase of the bit-detected reference signal 574 yieldingthe modified clock signal 572. Other implementations of the presentlydisclosed technology may utilize a delay-locked loop (DLL) or othercontrol system in place of PLL 566.

Read sensor 516 directly transmits incoming data bits 576 read off amedia to off-head electronics 568. With regard to writing outgoing databits, the implementation illustrated in FIG. 5 shows the bit-detectedreference signal 574 comes from a bit detector 550 (e.g. a waveformsensor, spin angular momentum sensor, tunneling current sensor, orcapacitance sensor) on the transducer head 520 that indicates patternedbit timing and the clock signal indicates timing for the writer. Thebit-detected reference signal 574 and the clock signal are compared todetermine a phase relationship between the clock signal and actualphysical positions of patterned bits on a media. The PLL 566 generates amodified clock signal 572 that is phase and frequency synchronized withactual physical positions of the patterned bits.

In one implementation, the PLL 566 has a high frequency oscillator,which generates the clock signal for the intended frequency of writing.The bit-detected reference signal 574 from the bit detector 550 iscompared to the clock signal and the phase between the bit-detectedreference signal 574 and the clock signal is measured and passed througha low pass filter to generate a DC bias. The DC bias is then applied tothe oscillator to change the frequency and phase of the clock signal tosynchronize the clock signal with the bit-detected reference signal 574.The synchronized clock signal (i.e. modified clock signal 572) is thensent to off-head electronics 568 in order to generate a write signal 576that is transmitted to a writer 518 that writes each outgoing data bitto the desired patterned bit on the media.

An advantage of using an on-head PLL 566 is faster detection of thephase difference between the clock signal and the actual frequency ofpatterned bits passing under the transducer head 520. On the contrary,an off-head PLL requires larger signal transit times resulting indetected phase information that may be outdated by the time PLLprocessing is completed. Further, in one implementation, on-head PLL 566enables low frequency bias information to be transmitted to off-headelectronics 568 instead of high frequency clock signals, which are moresusceptible to signal loss.

FIG. 6 is a flow diagram illustrating an on-head phase-locked loop 666(PLL) control scheme with an on-head write driver 670. Similar to FIG.5, read sensor 616 directly transmits incoming data bits 676 read off amedia to off-head electronics 668. With regard to writing outgoing databits 678, the PLL circuit on the transducer head of FIG. 5 may becombined with a write driver 670 on the transducer head 620 for betterwrite synchronization. The write driver 670 may write outgoing data bits678 received from an external connection to the off-head electronics 668directly to the writer 618. The write driver 670 is coupled to the PLL666 using on-head connections so that the phase information (e.g.modified clock signal 672) is directly transmitted to the write driver670 enabling the outgoing data bits 678 to be precisely written topatterned bits on a media.

An advantage of using an on-head write driver 670 is that delays andtiming errors that occur due to transmission of the modified clocksignal 672 to the off-head electronics 668 and transmission of the writesignal 676 from the off-head electronics 668 are reduced or eliminated.Further, using the on-head write driver 670 decreases time between phasedetection and the writing of data bits, resulting in a reducedlikelihood of errors.

The PLL 666 and write driver 670 may be physically positioned anywherein the transducer head 620. In one implementation, the PLL 666 and writedriver 670 are coupled together near the writer 618. In anotherimplementation, the PLL 666 is positioned near the writer 618 and thewrite driver 670 is positioned closer to a transducer head substrate sothat heat generated by the write driver 670 is dissipated through thetransducer head substrate. In higher power electronics, this orientationmay be desirable.

One implementation of the on-head PLL 666 with on-head write driver 670also incorporates an on-head data buffer. The combination of the on-headPLL 666, write driver 670, and data buffer is a self contained writercontrol system where the location and phase of the patterned bits on themedia are detected and the next data bit can be quickly written to thecorrect patterned bit. More specifically, a modified clock signal 672generated by the PLL 666 is sent to the write driver 670. Digital databits sent from the off-head electronics 668 to the data buffer areconverted to an analog data signal that is synchronized with themodified clock signal 672 and applied to the writer 618 with correctpolarity and phase.

An advantage of using an on-head data buffer is reduced time delay inconverting digital data bits to an analog data signal and reduced timedelay between patterned bit detection and bit writing, resulting inreduced probability of write errors.

Further, the on-head PLL 666, write driver 670, and data buffer may bepositioned at any location on the transducer head 620 so long as heatdissipation requirements are met and suitable electrical connectionsbetween the PLL 666, write driver 670, and data buffer are possible. Inone implementation, the PLL 666, write driver 670, and data buffer arecoupled together in one location. In other implementations, the PLL 666,write driver 670, and data buffer are in separate locations on thetransducer head 620. In still further implementations, the PLL 666,write driver 670, and/or data buffer may be located off-head so long asat least one of the PLL 666, write driver 670, and data buffer islocated on-head.

FIG. 7 is a flow chart illustrating operations 700 for using an on-headphase-locked loop (PLL) and an on-head write driver to synchronizewriting of data bits to patterned bits on a media. A bit detectordetects a signal that corresponds to positions of the patterned bits onthe media with respect to a writer on a transducer head 705. Thedetected signal, referred to herein as a bit-detected reference signal,is then sent from the bit detector to an on-head PLL circuit 710. A PLLis then applied to a clock signal corresponding to writer timing and thebit-detected reference signal to generate a modified clock signal thatis synchronized with actual positions of the patterned bits on the media715.

The modified clock signal is then sent to an on-head write driver 720.Further, data bits to be written to the patterned bits on the media aresent from off-head electronics to the on-head write driver 725. Thewrite driver then generates a write signal that incorporates the databits into the modified clock signal 730. The write signal is then sentfrom the write driver to a writer that transfers the data bits to thepatterned bits on the media 735.

FIG. 8 illustrates a plan view of an example disc drive 800. The discdrive 800 includes a base 802 to which various components of the discdrive 800 are mounted. A top cover 804, shown partially cut away,cooperates with the base 802 to form an internal, sealed environment forthe disc drive in a conventional manner. The components include aspindle motor 806 that rotates one or more storage medium discs 808 at aconstant high speed. Information is written to and read from tracks onthe discs 808 through the use of an actuator assembly 810, which rotatesduring a seek operation about a bearing shaft assembly 812 positionedadjacent the discs 808. The actuator assembly 810 includes a pluralityof actuator arms 814 that extend towards the discs 808, with one or moreflexures 816 extending from each of the actuator arms 814. Mounted atthe distal end of each of the flexures 816 is a head 818 that includesan air bearing slider enabling the head 818 to fly in close proximityabove the corresponding surface of the associated disc 808. The distancebetween the head 818 and the storage media surface during flight isreferred to as the fly height

During a seek operation, the track position of the head 818 iscontrolled through the use of a voice coil motor (VCM) 824, whichtypically includes a coil 826 attached to the actuator assembly 810, aswell as one or more permanent magnets 828 which establish a magneticfield in which the coil 826 is immersed. The controlled application ofcurrent to the coil 826 causes magnetic interaction between thepermanent magnets 828 and the coil 826 so that the coil 826 moves inaccordance with the well-known Lorentz relationship. As the coil 826moves, the actuator assembly 810 pivots about the bearing shaft assembly812 and the transducer heads 818 are caused to move across the surfacesof the discs 808.

The spindle motor 806 is typically de-energized when the disc drive 800is not in use for extended periods of time. The transducer heads 818 aremoved away from portions of the disc 808 containing data when the drivemotor is de-energized. The transducer heads 818 are secured overportions of the disc 808 not containing data through the use of anactuator latch arrangement and/or ramp assembly 844, which preventsinadvertent rotation of the actuator assembly 810 when the drive discs808 are not spinning.

A flex assembly 830 provides the requisite electrical connection pathsfor the actuator assembly 810 while allowing pivotal movement of theactuator assembly 810 during operation. The flex assembly 830 includes aprinted circuit board 834 to which a flex cable connected with theactuator assembly 810 and leading to the head 818 is connected. The flexcable may be routed along the actuator arms 814 and the flexures 816 tothe transducer heads 818. The printed circuit board 834 typicallyincludes circuitry for controlling the write currents applied to thetransducer heads 818 during a write operation and a preamplifier foramplifying read signals generated by the transducer heads 818 during aread operation. The flex assembly 830 terminates at a flex bracket forcommunication through the base deck 802 to a disc drive printed circuitboard (not shown) mounted to the bottom side of the disc drive 800.

In one implementation, a phase-locked loop circuit is mounted on thetransducer head 818 and configured to send a modified clock signal tothe printed circuit board 834 via flex assembly 830. Further, a writermounted on the transducer head 818 is configured to receive a writesignal from the printed circuit board 834 via flex assembly 830 andtransfer data to the disc 808 or any other media. In anotherimplementation, a write driver is mounted on the transducer head 818 andconfigured to receive outgoing data bits from the printed circuit board834 via flex assembly 830. The write driver then generates a writesignal that is sent to a writer which in turn transfers the outgoingdata bits to the disc 808.

The above specification and examples provide a complete description ofthe structures of exemplary implementations of apparatus that may beused for waveform based bit detection for bit patterned media. Althoughvarious implementations of the apparatus have been described above witha certain degree of particularity, or with reference to one or moreindividual implementations, those skilled in the art could make numerousalterations to the disclosed implementations without departing from thespirit or scope of the presently disclosed technology. It is intendedthat all matter contained in the above description and shown in theaccompanying drawings shall be interpreted as illustrative only ofparticular implementations and not limiting. The implementationsdescribed above and other implementations are within the scope of thefollowing claims.

What is claimed:
 1. An apparatus comprising: an on-head bit detectorlocated on a transducer head and configured to detect a referencesignal; and on-head control system circuitry integrated within thetransducer head and configured to synchronize a clock signal with thebit-detected reference signal.
 2. The apparatus of claim 1, wherein theon-head control system circuitry includes a phase-locked loop circuit.3. The apparatus of claim 1, wherein a data buffer of the on-headcontrol system circuitry is configured to convert a digital data signalto an analog data signal that is incorporated into the modified clocksignal.
 4. The apparatus of claim 1, wherein a modified clock signal isgenerated by passing a phase difference between the detected referencesignal and the clock signal through an on-head low pass filter togenerate a DC bias and the DC bias is applied to a high frequencyoscillator to change the frequency and phase of the clock signal.
 5. Theapparatus of claim 1, further comprising: an on-head writer configuredto record data received from off-head electronics to the bit locationson the storage device using the modified clock signal; and an on-headwrite driver configured to generate a write signal incorporating thedata into the modified clock signal and send the write signal to theon-head writer.
 6. A transducer head comprising: an on-head bit detectorlocated on a transducer head and configured to detect a referencesignal; and an on-head control system circuit integrated within thetransducer head and configured to synchronize a clock signal with thebit-detected reference signal to generate a modified clock signal thatis synchronized with the bit locations.
 7. The transducer head of claim6, wherein the control system circuitry includes a phase-locked loopcircuit.
 8. The transducer head of claim 6, wherein the on-head bitdetector includes a waveform sensor.
 9. The transducer head of claim 6,wherein the on-head bit detector includes a spin angular momentumsensor.
 10. The transducer head of claim 6, wherein the on-head bitdetector includes a tunneling current sensor.
 11. The transducer head ofclaim 6, further comprising: an on-head writer configured to record datareceived from off-head electronics to the bit locations on the storagedevice; and an on-head write driver configured to generate a writesignal incorporating the data into the modified clock signal and sendthe write signal to the on-head writer, wherein one or more of theon-head bit detector, on-head control system circuit, and the on-headwriter are fabricated in place on the transducer head during transducerhead manufacturing.
 12. The transducer head of claim 6, wherein amodified clock signal is generated by passing a phase difference betweenthe bit-detected reference signal and the clock signal through a lowpass filter to generate a DC bias and the DC bias is applied to a highfrequency oscillator to change the frequency and phase of the clocksignal.
 13. A transducer head comprising: an on-head bit detectorlocated on a transducer head and configured to detect a reference signalcorresponding to bit locations on a storage device; and on-head controlcircuitry integrated within the transducer head and configured tosynchronize a clock signal with the bit-detected reference signal. 14.The transducer head of claim 13, wherein the on-head bit detectorincludes a waveform sensor.
 15. The transducer head of claim 13, whereinthe on-head bit detector includes a spin angular momentum sensor. 16.The transducer head of claim 13, wherein the on-head bit detectorincludes a tunneling current sensor.
 17. The transducer head of claim13, further comprising: an on-head writer configured to record datareceived from off-head electronics to the bit locations on the storagedevice using the modified clock signal; and an on-head write driverconfigured to generate a write signal incorporating the data into themodified clock signal and send the write signal to the on-head writer.18. The transducer head of claim 17, wherein one or more of the of theon-head bit detector, on-head write driver, and on-head writer arefabricated in place on the transducer head during transducer headmanufacturing.
 19. The transducer head of claim 13, wherein the databits are in a digital signal, further comprising: a data bufferconfigured to convert the digital data to an analog data signal; whereinthe on-head write driver is further configured to receive the analogdata signal from the data buffer and incorporate the analog data signalinto the write signal.
 20. The transducer head of claim 13, wherein thewrite driver is integrated within the transducer head.